JP7829157B2 - Composite components - Google Patents

Description

This invention relates to composite members.

Ceramics are known for their high strength and heat resistance, but also for their resistance to deformation. Therefore, when a load is applied to ceramics, their ability to relieve the load is limited, which can lead to sudden fracture. To improve these properties, research has been actively conducted to enhance the strength of ceramics by incorporating fibers.

Patent Document 1 discloses a cement admixture containing a masterbatch (A) containing cellulose nanofibers obtained by micronizing cellulose in a polyester resin, a maleic anhydride copolymer resin (B), and water (C). It is described that by adding this cement admixture to a cement composition, cellulose nanofibers can be uniformly dispersed in the cement composition, and as a result, the strength of cement molded articles such as concrete and mortar is improved.

Japanese Patent Publication No. 2015-155357

However, since cement molded bodies are mainly composed of hydrates and have many pores, even if fibers are incorporated, there was a problem in that the resulting molded bodies had insufficient mechanical strength.

This invention has been made in view of the problems of the prior art. The object of this invention is to provide a composite member with excellent mechanical strength.

To solve the above problems, a composite member according to an embodiment of the present invention comprises an inorganic matrix portion composed of an inorganic substance containing a metal hydroxide, and metal fibers dispersed within the inorganic matrix portion having an aspect ratio of 100 or more. Furthermore, the porosity of the cross-section of the inorganic matrix portion is 20% or less.

Figure 1 is a schematic cross-sectional view showing an example of a composite member according to this embodiment. Figure 2(a) is a schematic diagram showing an enlarged cross-section of the composite member shown in Figure 1. Figure 2(b) is a schematic cross-sectional view showing the vicinity of the grain boundary of a group of inorganic material particles. Figure 3 shows scanning electron microscope (SEM) images of the cross-sections of the test samples from Example 1-2, observed at 1000x and 3000x magnification. The left column shows the backscattered electron image of the test sample's cross-section, and the right column shows the binarized data of the backscattered electron image. Figure 4 is a scanning electron microscope image showing the results of observing the cross-section of the test samples from Example 1-2 at a magnification of 500x. Figure 5A is a scanning electron microscope image showing the results of observing a cross-section of a sample of aluminum fiber embedded in resin, as used in Examples 1-1 to 1-3, at a magnification of 1000x. Figure 5B is a scanning electron microscope image showing the results of observing a cross-section of a sample of aluminum fiber embedded in resin, as used in Examples 1-1 to 1-3, at a magnification of 3000x. Figure 6A is a scanning electron microscope image showing the results of observing the cross-sections of the test samples of Comparative Examples 1-3 at a magnification of 1000x. Figure 6B is a scanning electron microscope image showing the results of observing the cross-sections of the test samples of Comparative Examples 1-3 at a magnification of 3000x. Figure 7 is a graph showing the relationship between stroke displacement and load when bending strength was measured in accordance with JIS T6526 for the test samples of Example 2-1 and Comparative Examples 2-1 and 2-2. Figure 8(a) is a photograph showing the test sample of Example 2-1 after bending strength measurement. Figure 8(b) is a photograph showing the test sample of Comparative Example 2-2 after bending strength measurement. Figure 9 shows scanning electron microscope images of aluminum fibers before hydrothermal treatment according to Reference Example 3-1, aluminum fibers after hydrothermal treatment according to Reference Example 3-2, and aluminum fibers after ammonium-added hydrothermal treatment according to Reference Example 3-3, observed at magnifications of 1000x and 3000x, respectively. Figure 10 is a graph showing the results of X-ray diffraction measurement of the surface of aluminum fibers after hydrothermal treatment according to Reference Example 3-2. Figure 11 is a graph showing the X-ray diffraction pattern of hydraulic alumina, as well as the patterns of boehmite (AlOOH) and gibbsite (Al(OH) ₃ ) registered in ICSD. Figure 12 is a graph showing the X-ray diffraction pattern of the test sample of Reference Example 4, as well as the X-ray diffraction patterns of boehmite and gibbsite registered in ICSD.

The composite member according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[Composite materials]
As shown in Figure 1, the composite member 100 of this embodiment comprises an inorganic matrix portion 10 composed of an inorganic substance and metal fibers 20 dispersed within the inorganic matrix portion 10.

The inorganic matrix portion 10 is composed of a plurality of particles 11 made of inorganic material, and the inorganic matrix portion 10 is formed by the bonding of the inorganic material particles 11 with each other.

The inorganic material constituting the inorganic matrix portion 10 preferably contains at least one metallic element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals, and metalloids. In this specification, alkaline earth metals include calcium, strontium, barium, and radium, as well as beryllium and magnesium. Base metals include aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium, lead, bismuth, and polonium. Metalloids include boron, silicon, germanium, arsenic, antimony, and tellurium. Among these, the inorganic material preferably contains at least one metallic element selected from the group consisting of aluminum, iron, nickel, gallium, and yttrium.

The inorganic substance constituting the inorganic matrix portion 10 contains the hydroxide oxide of the above-mentioned metal element. Furthermore, it is preferable that the inorganic substance mainly contains the hydroxide oxide of the above-mentioned metal element. In other words, it is preferable that the inorganic substance contains 50 mol% or more of the hydroxide oxide of the above-mentioned metal element, and more preferably 80 mol% or more. Since such an inorganic substance has high stability against oxygen and water vapor in the atmosphere, by arranging the metal fibers 20 inside the inorganic matrix portion 10, contact between the metal fibers 20 and oxygen and water vapor can be suppressed, thereby suppressing the deterioration of the metal fibers 20. Note that when the inorganic substance mainly consists of the hydroxide oxide of the above-mentioned metal element, the inorganic substance may also contain the hydroxide of the above-mentioned metal element.

Furthermore, the inorganic matrix portion 10 is preferably polycrystalline. That is, the inorganic material particles 11 are preferably crystalline particles, and the inorganic matrix portion 10 is preferably formed by the aggregation of many particles 11. By making the inorganic matrix portion 10 polycrystalline, a composite member 100 with higher durability can be obtained compared to the case where it is amorphous. It is more preferable that the inorganic material particles 11 are crystalline particles containing at least one metal element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals, and metalloids. Furthermore, it is preferable that the inorganic material particles 11 are crystalline particles containing the hydroxide oxide of the above metal element. It is more preferable that the inorganic material particles 11 are crystalline particles mainly composed of the hydroxide oxide of the above metal element.

The metal hydroxide contained in the inorganic material of the inorganic matrix portion 10 may include aluminum. Furthermore, the metal hydroxide is preferably boehmite. Boehmite is an aluminum hydroxide represented by the chemical formula AlOOH. Boehmite is insoluble in water and hardly reacts to acids and alkalis at room temperature, thus possessing high chemical stability. It also has excellent heat resistance due to its high dehydration temperature of around 500°C. Additionally, since boehmite has a specific gravity of approximately 3.07, when the inorganic matrix portion 10 is made of boehmite, a lightweight and chemically stable composite member 100 can be obtained.

When the inorganic substance constituting the inorganic matrix portion 10 is boehmite, the particles 11 may consist only of the boehmite phase, or they may consist of a mixed phase of boehmite and aluminum oxide or aluminum hydroxide other than boehmite. For example, the particles 11 may be a mixture of a phase consisting of boehmite and a phase consisting of gibbsite (Al(OH) ₃ ). In this case, it is preferable that adjacent particles 11 are bonded together via a bonding portion 30 consisting of at least one of aluminum oxide and aluminum hydroxide. In other words, it is preferable that the particles 11 are not bonded together by an organic binder made of an organic compound, nor by an inorganic binder made of an inorganic compound other than aluminum oxide and aluminum hydroxide. When adjacent particles 11 are bonded together via a bonding portion 30 consisting of at least one of aluminum oxide and aluminum hydroxide, the aluminum oxide and aluminum hydroxide may be crystalline or amorphous.

When the inorganic matrix portion 10 is made of boehmite, the proportion of the boehmite phase is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. By increasing the proportion of the boehmite phase, an inorganic matrix portion 10 that is lightweight and has excellent chemical stability and heat resistance can be obtained. The proportion of the boehmite phase in the inorganic matrix portion 10 can be determined by measuring the X-ray diffraction pattern of the inorganic matrix portion 10 by X-ray diffraction and then performing Rietveld analysis.

The average particle diameter of the inorganic material particles 11 constituting the inorganic matrix portion 10 is not particularly limited. However, the average particle diameter of the particles 11 is preferably 300 nm or more and 50 μm or less, more preferably 300 nm or more and 30 μm or less, even more preferably 300 nm or more and 10 μm or less, and particularly preferably 300 nm or more and 5 μm or less. By having the average particle diameter of the inorganic material particles 11 within this range, the particles 11 are strongly bound together, and the strength of the inorganic matrix portion 10 can be increased. Furthermore, by having the average particle diameter of the inorganic material particles 11 within this range, as will be described later, the proportion of pores present inside the inorganic matrix portion 10 can be reduced to 20% or less. In this specification, unless otherwise specified, the value of "average particle diameter" is the value calculated as the average value of the particle diameters of particles observed in several to tens of fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

The shape of the inorganic particles 11 is not particularly limited, but they can be spherical, for example. The particles 11 may also be whisker-shaped (needle-shaped) or flaky. Whisker-shaped or flaky particles have higher contact with other particles compared to spherical particles, which tends to improve the strength of the inorganic matrix portion 10. Therefore, by using particles of this shape as the particles 11, it is possible to increase the overall strength of the composite member 100.

As described above, it is more preferable that the inorganic substance constituting the inorganic matrix portion 10 contains metal hydroxide as its main component. Therefore, it is preferable that the inorganic matrix portion 10 also has metal hydroxide as its main component. In other words, it is preferable that the inorganic matrix portion 10 contains 50 mol% or more of metal hydroxide, and more preferably 80 mol% or more.

Furthermore, it is preferable that the inorganic substance constituting the inorganic matrix portion 10 is substantially free of hydrates. In this specification, "substantially free of hydrates" means that the inorganic substance is not intentionally made to contain hydrates. Therefore, if hydrates are inevitably mixed into the inorganic substance as impurities, the condition "substantially free of hydrates" is met. Note that since boehmite is a metal hydroxide, it is not included in the definition of hydrates in this specification.

Furthermore, it is preferable that the inorganic material constituting the inorganic matrix portion 10 does not contain hydrates of calcium compounds. The calcium compounds referred to here are tricalcium silicate (alite, 3CaO・_SiO₂ ), dicalcium silicate (beelite, 2CaO・_SiO₂ ), calcium _{aluminate (} 3CaO・_Al₂O₃ ), calcium aluminoferrite (4CaO・_Al₂O₃・_Fe₂O₃ ), and calcium sulfate ( _CaSO₄・_2H₂O ). If the _inorganic material constituting the inorganic matrix portion 10 contains hydrates of the above calcium compounds, the resulting composite member may have a porosity exceeding 20% in the cross-section of the inorganic matrix portion. Therefore, it is preferable that the inorganic material does not contain hydrates of the above calcium compounds. Furthermore, it is preferable that the inorganic material constituting the inorganic matrix portion 10 does not contain phosphate cement, zinc phosphate cement, and calcium phosphate cement. By not including these cements in the inorganic material, it is possible to reduce the porosity of the resulting composite member to 20% or less.

The composite member 100 comprises metal fibers 20 made of metal. The metal fibers 20 are dispersed inside the inorganic matrix portion 10 and are fixed in contact with the inorganic matrix portion 10. As the metal fibers 20, those made entirely of pure metal or alloy can be used, or those using resin as the core and coated with metal as the sheath portion can be used. However, in this embodiment, it is preferable that the metal fibers 20 are made of pure metal or alloy.

The metal constituting the metal fiber 20 can be at least one metallic element selected from the group consisting of, for example, gold, silver, copper, platinum, iridium, palladium, ruthenium, rhodium, titanium, aluminum, tantalum, niobium, tungsten, molybdenum, vanadium, magnesium, chromium, iron, cobalt, nickel, zinc, tin, and lead. The metal constituting the metal fiber 20 may be these metallic elements in their individual components, or it may be an alloy of these metallic elements in any combination.

The metal fibers 20 are preferably malleable. As will be described later, the composite member 100 can be manufactured by a pressurized heating method. Because the metal fibers 20 are malleable, they plastically deform along the shape of the particles 11 when pressurized, and can therefore adhere to the particles 11 of the inorganic matrix portion 10. Examples of metals with high malleability include gold, silver, lead, copper, and aluminum. Therefore, the metal fibers 20 are preferably fibers made of gold, silver, lead, copper, or aluminum, or fibers made of an alloy containing at least one of gold, silver, lead, copper, or aluminum.

Furthermore, it is preferable that the metal fibers 20 are ductile. As described above, the inorganic matrix portion 10 itself is formed by the bonding of inorganic material particles 11, and therefore has high hardness but is prone to brittle fracture. However, because the metal fibers 20 are ductile, when an external force is applied to the inorganic matrix portion 10, the metal fibers 20 can be stretched within the inorganic matrix portion 10. As a result, brittle fracture of the inorganic matrix portion 10 is suppressed, and the occurrence of cracks and the like is suppressed, so the bending stress of the composite member can be increased and the mechanical strength can be improved. Examples of metals that are highly ductile include gold, silver, platinum, iron, and nickel. Therefore, it is also preferable that the metal fibers 20 are fibers made of gold, silver, platinum, iron, and nickel, or fibers made of an alloy containing at least one of gold, silver, platinum, iron, and nickel.

The aspect ratio (fiber length/fiber diameter) of the metal fibers is preferably 100 or more, more preferably 200 or more, even more preferably 500 or more, and particularly preferably 1000 or more. The fiber diameter of the metal fibers 20 is not particularly limited, but can be between 1 μm and 100 μm. A larger aspect ratio of the metal fibers 20 makes it easier for the inorganic material particles 11 to connect with each other via the metal fibers 20. Therefore, even when an external force is applied to the inorganic matrix portion 10, the occurrence of cracks can be suppressed. Furthermore, even if cracks do occur in the inorganic matrix portion 10, the metal fibers 20 can be dispersed to connect the crack surfaces and suppress the fracture of the inorganic matrix portion 10.

In the composite member 100, the metal fibers 20 may be mainly oriented in a predetermined direction within the inorganic matrix portion 10. Here, "the metal fibers are mainly oriented in a predetermined direction" means that when the composite member 100 is observed using a microscope, more than half of the multiple fibers visible in the field of view are oriented in substantially the same specific direction. For example, if the composite member 100 is plate-shaped, the metal fibers 20 may be mainly oriented parallel to the surface (main surface) within the inorganic matrix portion 10. Also, if the composite member 100 is rod-shaped, the metal fibers 20 may be mainly oriented in the longitudinal direction within the inorganic matrix portion 10. In this way, because the metal fibers 20 in the composite member 100 are oriented in a predetermined direction, the metal fibers 20 can be stretched when an external force is applied from a direction perpendicular to that predetermined direction. As a result, the bending stress of the composite member 100 increases, and thus the mechanical strength can be improved.

In the composite member 100, the metal fibers 20 can be present in a composition of 10% by volume or more. The higher the content of metal fibers 20 in the composite member 100, the higher the bending stress of the composite member 100 can be. Therefore, from the viewpoint of increasing the mechanical strength of the composite member 100, it is preferable that the lower limit of the content of metal fibers 20 in the composite member 100 be 10% by volume. Furthermore, it is preferable that the lower limit of the content of metal fibers 20 in the composite member 100 be 20% by volume, and more preferably 30% by volume. In addition, it is preferable that the upper limit of the content of metal fibers 20 in the composite member 100 be 80% by volume, and more preferably 70% by volume.

In the composite member 100, the metal hydroxide and the metal fibers 20 can contain the same metal element. Specifically, both the metal hydroxide and the metal fibers 20 can contain aluminum. When the metal hydroxide contains aluminum, the inorganic matrix portion 10 can be made of boehmite. When the metal fibers 20 contain aluminum, the metal fibers 20 can be made of pure aluminum or an aluminum alloy. When the metal fibers 20 contain aluminum, a boehmite layer is formed on the surface of the metal fibers during the manufacturing of the composite member 100, allowing the inorganic matrix portion 10 and the metal fibers 20 to be fixed together.

In the composite member 100, the inorganic matrix portion 10 and the metal fibers 20 can be configured such that they are formed on the surface of the metal fibers 20 and are fixed to each other via a boehmite layer different from the inorganic matrix portion 10. As will be described later, the composite member 100 can be obtained by mixing a precursor of the inorganic substance constituting the inorganic matrix portion 10, metal fibers, and a solvent to obtain a mixture, and then pressurizing and heating the mixture at 50 to 300°C and 10 to 600 MPa. Specifically, when the inorganic matrix portion 10 is made of boehmite, the composite member 100 can be obtained by mixing hydraulic alumina, metal fibers, and water to obtain a mixture, and then pressurizing and heating the mixture at 50 to 300°C and 10 to 600 MPa.

Here, if the metal fibers contain aluminum, during the pressurizing and heating process, the aluminum oxide (anodized aluminum) and/or aluminum on the surface of the metal fibers react with water, forming a layer of boehmite on the surface of the metal fibers. Therefore, when the inorganic matrix portion 10 is made of boehmite, the affinity between the particles 11 and the boehmite layer on the surface of the metal fibers 20 increases, allowing the particles 11 and the metal fibers 20 to adhere to each other via the formed boehmite layer. Furthermore, the boehmite layer absorbs the shear force generated between the inorganic matrix portion 10 and the metal fibers 20, suppressing their separation. Moreover, the aluminum constituting the metal fibers 20 also possesses excellent ductility. Therefore, even when an external force is applied to the inorganic matrix portion 10, the effect of the aluminum fibers suppresses the occurrence of cracks and other damage, and increases the bending stress.

In the composite member 100, it is preferable that the porosity of the inorganic matrix portion 10 in cross-section is 20% or less. That is, when observing the cross-section of the inorganic matrix portion 10, it is preferable that the average value of the pore ratio per unit area is 20% or less. When the porosity is 20% or less, the metal fibers 20 can be sealed inside the dense inorganic material. Therefore, the contact rate between oxygen and water vapor from outside the composite member 100 and the metal fibers 20 is reduced, making it possible to suppress the oxidation of the metal fibers 20 over a long period of time. Furthermore, in this case, since the inorganic matrix portion 10 has few pores inside and the inorganic material is dense, the composite member 100 can have high strength. It is preferable that the porosity of the inorganic matrix portion 10 in cross-section is 15% or less, more preferably 10% or less, and even more preferably 5% or less. The smaller the porosity of the inorganic matrix portion 10 in cross-section, the more the contact between the metal fibers 20 and oxygen and water vapor is suppressed, thus preventing the deterioration of the metal fibers 20.

In this specification, porosity can be determined as follows. First, the cross-section of the inorganic matrix portion 10 is observed to distinguish between the inorganic matrix portion 10, the metal fibers 20, and the pores. Then, the area of pores per unit area is measured, and the ratio of pores per unit area is determined. After determining the ratio of pores per unit area at multiple locations, the average value of the ratio of pores per unit area is taken as the porosity. When observing the cross-section of the inorganic matrix portion 10, an optical microscope, a scanning electron microscope (SEM), or a transmission electron microscope (TEM) can be used. In addition, the area of pores per unit area and the area of pores per unit area may be measured by binarizing the image observed with a microscope.

The shape of the composite member 100 is not particularly limited, but it can be, for example, plate-shaped. The thickness t of the composite member 100 is also not particularly limited, but it can be, for example, 50 μm or more. As will be described later, since the composite member 100 is formed by a pressurized heating method, composite members 100 with large thicknesses can be easily obtained. The thickness t of the composite member 100 can be 1 mm or more, and can also be 1 cm or more. The upper limit of the thickness t of the composite member 100 is not particularly limited, but it can be, for example, 50 cm.

As described above, the composite member 100 of this embodiment comprises an inorganic matrix portion 10 composed of an inorganic substance containing a metal hydroxide, and metal fibers 20 dispersed within the inorganic matrix portion 10 with an aspect ratio of 100 or more. Furthermore, in the composite member 100, the porosity of the cross-section of the inorganic matrix portion 10 is 20% or less. In the composite member 100, since the metal fibers 20 are dispersed within the inorganic matrix portion 10, the inorganic substance particles 11 are connected by the metal fibers 20, thereby increasing the bending strength and mechanical strength of the composite member 100. Moreover, since the porosity of the cross-section of the composite member 100 is 20% or less, contact between oxygen and water vapor and the metal fibers 20 is suppressed, and the metal fibers 20 can be stably dispersed over a long period of time.

[Method for manufacturing composite components]
Next, a method for manufacturing the composite member according to this embodiment will be described. The composite member 100 can be manufactured by heating a mixture of precursor particles of an inorganic substance constituting the inorganic matrix portion 10 and metal fibers under pressure while containing a solvent. By using such a pressurized heating method, the precursor particles of the inorganic substance react with the solvent and bond together, thereby forming an inorganic matrix portion 10 in which the metal fibers 20 are dispersed inside.

Specifically, first, a mixture is prepared by mixing a powder of the precursor of the inorganic substance constituting the inorganic matrix portion 10 with metal fibers. The powder of the inorganic substance precursor and the metal fibers may be mixed in air or in an inert atmosphere. As the precursor of the inorganic substance constituting the inorganic matrix portion 10, a material that generates a metal oxide hydroxide when heated and pressurized with a solvent is used. For example, if the inorganic substance constituting the inorganic matrix portion 10 is boehmite, hydraulic alumina can be used as the precursor of the inorganic substance.

Next, a solvent is added to the mixture. The solvent used is one that reacts with the inorganic precursor to produce a metal hydroxide oxide. Such a solvent can be at least one selected from the group consisting of water, acidic aqueous solutions, alkaline aqueous solutions, alcohols, ketones, and esters. As the acidic aqueous solution, an aqueous solution with a pH of 1 to 3 can be used. As the alkaline aqueous solution, an aqueous solution with a pH of 10 to 14 can be used. It is preferable to use an aqueous solution of an organic acid as the acidic aqueous solution. Furthermore, it is preferable to use an alcohol having 1 to 12 carbon atoms.

Next, a mixture containing an inorganic substance precursor, metal fibers, and a solvent is filled into the mold. After filling the mold with the mixture, the mold may be heated as needed. Then, by applying pressure to the mixture inside the mold, the inside of the mold becomes a high-pressure state. At this time, the inorganic substance precursor and metal fibers become densified, the particles of the inorganic substance precursor bond together, and at the same time, the inorganic substance precursor reacts with the solvent to form metal hydroxide. As a result, the metal fibers 20 can be dispersed inside the inorganic matrix portion 10 composed of metal hydroxide.

The pressurized heating conditions for a mixture containing an inorganic substance, metal fibers, and a solvent are not particularly limited, as long as the conditions allow the solvent to react with the inorganic substance precursor to produce a metal hydroxide oxide. For example, it is preferable to heat the mixture containing the inorganic substance precursor, metal fibers, and solvent to 50 to 300°C, and then pressurize it to a pressure of 10 to 600 MPa. The temperature when heating the mixture containing the inorganic substance, metal fibers, and solvent is more preferably 80 to 250°C, and even more preferably 100 to 200°C. Furthermore, the pressure when pressurizing the mixture containing the inorganic substance, metal fibers, and solvent is more preferably 50 to 600 MPa, and even more preferably 200 to 600 MPa.

Then, by removing the molded body from inside the mold, the composite member 100 can be obtained.

Here, we will describe a method for manufacturing a composite member 100 in which the inorganic substance constituting the inorganic matrix portion 10 is boehmite. The composite member 100 in which the inorganic substance is boehmite can be manufactured by mixing hydraulic alumina, which is a precursor of the inorganic substance, metal fibers, and a solvent containing water, and then heating under pressure. Hydraulic alumina is an oxide obtained by heat-treating aluminum hydroxide and contains ρ-alumina. Such hydraulic alumina has the property of bonding and hardening through a hydration reaction. Therefore, by using a pressurized heating method, the hydration reaction of hydraulic alumina proceeds, and the hydraulic alumina particles bond with each other, and the crystalline structure changes to boehmite, thereby forming the inorganic matrix portion 10.

Specifically, a mixture is first prepared by mixing hydraulic alumina powder, metal fibers, and a water-containing solvent. The water-containing solvent is preferably pure water or deionized water. However, the water-containing solvent may also contain acidic or alkaline substances in addition to water. Furthermore, the water-containing solvent only needs to have water as its main component; it may also contain organic solvents (such as alcohol).

The amount of solvent added to the hydraulic alumina is preferably an amount that allows the hydration reaction of the hydraulic alumina to proceed sufficiently. The amount of solvent added is preferably 20 to 200% by mass relative to the hydraulic alumina, and more preferably 50 to 150% by mass.

Next, a mixture of hydraulic alumina, metal fibers, and a water-containing solvent is filled into the mold. After filling the mold with this mixture, the mold may be heated as needed. By applying pressure to the mixture inside the mold, the inside of the mold becomes a high-pressure state. At this time, the hydraulic alumina becomes denser, and the hydraulic alumina particles bond with each other, resulting in increased density. Specifically, by adding water to the hydraulic alumina, a hydration reaction occurs, and boehmite and aluminum hydroxide are formed on the surface of the hydraulic alumina particles. Then, by heating and pressurizing the mixture inside the mold, the formed boehmite and aluminum hydroxide diffuse between adjacent hydraulic alumina particles, causing the hydraulic alumina particles to gradually bond with each other. Subsequently, as the dehydration reaction proceeds due to heating, the crystalline structure changes from aluminum hydroxide to boehmite. It is presumed that the hydration reaction of hydraulic alumina, the mutual diffusion between hydraulic alumina particles, and the dehydration reaction proceed almost simultaneously.

Then, by removing the molded body from inside the mold, a composite member 100 can be obtained in which multiple particles 11 are bonded together via at least one of aluminum oxide and aluminum hydroxide.

Thus, the manufacturing method for the composite member 100 includes a step of mixing an inorganic material precursor constituting the inorganic matrix portion 10, metal fibers, and a solvent for reacting with the inorganic material precursor to produce metal hydroxide oxides to obtain a mixture. The manufacturing method for the composite member 100 further includes a step of pressurizing and heating the mixture. The pressurizing and heating conditions for the mixture are preferably a temperature of 50 to 300°C and a pressure of 10 to 600 MPa. In the manufacturing method of this embodiment, since the composite member 100 is formed under such low-temperature conditions, deterioration of the metal fibers is suppressed, and a composite member 100 with excellent mechanical strength can be obtained.

Furthermore, in the manufacturing method of this embodiment, since the mixture obtained by mixing an inorganic substance precursor, metal fibers, and a solvent is heated and pressurized, the inorganic substance aggregates to form a dense inorganic matrix portion 10. As a result, the number of pores inside the inorganic matrix portion 10 is reduced, making it possible to obtain a composite member 100 with high strength while suppressing oxidative degradation of the metal fibers 20.

[Applications of composite materials]
Next, the applications of the composite member 100 according to this embodiment will be described. As described above, the composite member 100 has high mechanical strength and can be made into a plate with a large thickness, so it can be used in structures. Preferably, the structures that incorporate the composite member 100 are housing equipment, housing components, building materials, and buildings. Housing equipment, housing components, building materials, and buildings are structures that are in high demand in people's lives, so by using the composite member 100 in structures, it is possible to expect the creation of a new and large market.

The composite member of this embodiment can be used as a building component. In other words, the building component of this embodiment includes the composite member 100. A building component is a component manufactured for construction, and in this embodiment, the composite member 100 can be used in at least a part of it. As described above, the composite member 100 can be made into a thick plate and has high strength and durability. Therefore, the composite member 100 can be suitably used as a building component. Examples of building components include exterior wall materials (siding) and roofing materials. Other examples of building components include road materials and exterior drainage materials.

Furthermore, the composite member of this embodiment can also be used as an interior component. In other words, the interior component of this embodiment includes the composite member 100. Examples of interior components include bathtubs, kitchen counters, washbasins, and flooring materials.

The embodiment will be described in further detail below with reference to examples, comparative examples, and reference examples, but the embodiment is not limited to these examples.

[Example 1]
(Preparation of test samples)
<Example 1-1>
First, as the hydraulic alumina, Sumitomo Chemical Co., Ltd.'s hydraulic alumina BK-112 was prepared. The median particle size of this hydraulic alumina was approximately 16 μm. Analysis of the hydraulic alumina powder by powder X-ray diffraction revealed that it was a mixture of boehmite and gibbsite (aluminum hydroxide), as will be described later. Furthermore, the hydraulic alumina also contained ρ-alumina. In addition, aluminum fiber (product number: TW/Al/20) manufactured by Nikko Techno Co., Ltd. was prepared as the fiber material. The average fiber diameter of this aluminum fiber was approximately 20 μm, and the average fiber length was 5 mm or more.

Next, hydraulic alumina and aluminum fibers were weighed in such a ratio of hydraulic alumina:aluminum fibers = 90% by volume:10% by volume. The hydraulic alumina and aluminum fibers were then mixed using an agate mortar and pestle to obtain a mixed powder. Finally, ion-exchanged water was weighed in such a ratio of 80% by mass relative to the hydraulic alumina. The mixed powder and ion-exchanged water were then mixed using an agate mortar and pestle to obtain a mixture.

Next, the obtained mixture was placed inside a cylindrical molding die (Φ10) having an internal space. The mixture was then heated and pressurized under conditions of 400 MPa, 180°C, and 20 minutes to obtain the test sample for this example.

<Example 1-2>
The test sample for this example was obtained in the same manner as in Example 1-1, except that aluminum fibers were added in a ratio of hydraulic alumina:aluminum fibers = 80% by volume:20% by volume.

<Examples 1 and 3>
The test sample for this example was obtained in the same manner as in Example 1-1, except that aluminum fibers were added in a ratio of 50% by volume to 50% by volume of hydraulic alumina.

<Comparative Example 1-1>
The test sample for this example was obtained in the same manner as in Example 1-1, except that aluminum fibers were not added.

<Comparative Example 1-2>
Advanced Alumina AA-18 _, manufactured by Sumitomo Chemical Co., Ltd., was prepared as alumina powder ( _Al₂O₃ ). Advanced Alumina AA-18 is a single-crystal particle of α-alumina with a shape close to a polyhedral sphere, and its median particle size is approximately 20.3 μm. The test sample for this example was obtained in the same manner as in Examples 1-3, except that alumina powder was added instead of aluminum fibers.

<Comparative Example 1-3>
As the fiber material, Denka Arsen (registered trademark), an alumina fiber manufactured by Denka Co., Ltd., was prepared. The average fiber diameter of the alumina fiber was 3 to 5 μm. The test sample for this example was obtained in the same manner as in Example 1-2, except that alumina fiber was added instead of aluminum fiber.

Table 1 summarizes the type and amount of aggregate added to each test sample, as well as the relative density of each test sample. The relative density was calculated as follows.

First, the actual specific gravity was determined from the volume and mass of each test sample. Furthermore, the theoretical specific gravity of each test sample was determined from the proportions of boehmite and aggregate contained in each sample. Specifically, in Example 1-1, since boehmite was 90% by volume and aluminum fiber was 10% by volume, the theoretical specific gravity was determined from the proportions and specific gravities of boehmite and aluminum. Then, the relative density was defined as the actual specific gravity relative to the theoretical specific gravity ([actual specific gravity] / [theoretical specific gravity] × 100).

(Bending strength measurement)
The bending strength of each test sample was measured in accordance with the Japanese Industrial Standard JIS T6526:2018 (Dental Ceramic Materials). The bending strength of the test samples was measured using the biaxial bending test specified in JIS T6526. The maximum bending strength (stress) for each test sample is shown in Table 1.

Examples 1-1 to 1-3 and Comparative Example 1 show that adding aluminum fibers, which are metal fibers, increases bending stress and improves mechanical strength. In particular, Examples 1-3 and Comparative Example 1-1 show that when the aluminum fiber content is 50 volume%, the bending strength is nearly three times higher compared to when no aluminum fibers are added. Furthermore, Examples 1-1 to 1-3 show that the bending strength improves as the amount of aluminum fibers added increases. Therefore, it is presumed that the bending strength will be further improved by adding more than 50 volume% of aluminum fibers.

In contrast, Comparative Examples 1-1 and 1-2 show that adding alumina particles does not improve flexural strength, but rather significantly decreases it. Similarly, Comparative Examples 1-1 and 1-3 show that adding alumina fibers does not improve flexural strength, but rather significantly decreases it.

(Microscopic observation)
The test samples of Example 1-2 were observed in cross-section using a scanning electron microscope (SEM). Figure 3 is an SEM image showing the results of observing the cross-section of the test samples of Example 1-2 at magnifications of 1000x and 3000x. Figure 3 shows the cross-section of the aluminum fibers 20 present in the inorganic matrix portion 10. The black linear portion indicated by the symbol A in Figure 3 is a polishing scratch that occurred when the test sample was polished. As shown in Figure 3, there is almost no void between the inorganic matrix portion 10 and the aluminum fibers 20, and it can be seen that they are in close contact with each other. In other words, it can be seen that the aluminum fibers 20 adhere to the inorganic matrix portion 10 due to plastic deformation of the aluminum fibers 20 during the pressurization process.

Furthermore, Figure 3 also shows binarized images of backscattered electron images observed at 1000x and 3000x magnification. By binarizing the backscattered electron images, the pore areas can be clearly identified. In the binarized images, the black areas represent the inorganic matrix 10 and aluminum fibers 20, and the white areas represent pores. The area ratio of the pore areas was then calculated from the binarized images and defined as the porosity. As a result, the porosity of the backscattered electron image at 1000x magnification in Figure 3 was 0.226%, and the porosity of the backscattered electron image at 3000x magnification was 0.21%.

Figure 4 is an SEM image showing the results of observing the cross-section of the test sample from Example 1-2 at 500x magnification. The arrows in Figure 4 indicate the direction of pressure (pressing direction) when the mixture of hydraulic alumina, aluminum fibers, and ion-exchanged water is placed in a molding die and pressurized. As shown in Figure 4, there is almost no void between the inorganic matrix portion 10 and the aluminum fibers 20, indicating that they are in close contact with each other. Furthermore, it can be seen that the cross-section of the aluminum fibers 20 is flattened along a direction approximately perpendicular to the pressing direction. From this, it can be seen that the aluminum fibers 20 adhere to the inorganic matrix portion 10 due to plastic deformation caused by the pressing pressure.

For reference, Figure 5A shows the results of observing a cross-section of a sample in which aluminum fibers were embedded in resin at a magnification of 1000x. Figure 5B shows the results of observing a cross-section of a sample in which aluminum fibers were embedded in resin at a magnification of 3000x. In other words, Figures 5A and 5B show the cross-section of the aluminum fibers before the mixture of hydraulic alumina, aluminum fibers, and deionized water was placed in a molding die and pressurized. From Figures 4, 5A, and 5B, it can be seen that when the mixture is placed in a molding die and pressurized, the aluminum fibers undergo plastic deformation into a flattened shape due to the press pressure.

Figure 6A is an SEM image showing the results of observing the cross-section of the test samples of Comparative Examples 1-3 at a magnification of 1000x. Figure 6B is an SEM image showing the results of observing the cross-section of the test samples of Comparative Examples 1-3 at a magnification of 3000x. Figures 6A and 6B also show the cross-section of the alumina fibers 40 present in the inorganic matrix portion 10. As can be seen from Figures 6A and 6B, the alumina fibers 40 in the test samples of Comparative Examples 1-3 have not undergone plastic deformation into a flattened shape. Furthermore, it can be seen that numerous pores 42 exist between the inorganic matrix portion 10 and the alumina fibers 40.

(Vickers hardness measurement)
The Vickers hardness of the test samples from Examples 1-2 and Comparative Examples 1-3 was measured in accordance with JIS R1610 (Test Method for Hardness of Fine Ceramics). As a result, the Vickers hardness of the test sample from Example 1-2, which contained 20 volume% aluminum fibers, was 2.0 GPa. The Vickers hardness of the test sample from Comparative Examples 1-3, which contained 20 volume% alumina fibers, was 2.3 GPa.

(evaluation)
Since aluminum is a highly malleable metal, the aluminum fibers 20 can be fixed to the inorganic matrix portion 10 by plastic deformation, as shown in Figures 3 and 4. Furthermore, aluminum also possesses ductility. Therefore, by dispersing aluminum fibers in the inorganic matrix portion 10, the occurrence of cracks and other damage can be suppressed even when external forces are applied to the inorganic matrix portion 10. As a result, the bending stress of the composite member is increased, and its mechanical strength can be improved.

In contrast, since alumina is a material with low ductility, even if dispersed in the inorganic matrix 10, it is difficult to suppress the brittle fracture of the inorganic matrix 10. Furthermore, because alumina has low malleability, it is a material that does not easily undergo plastic deformation. Therefore, the inorganic matrix and alumina fibers do not adhere well, and numerous pores are generated between them. Thus, because alumina has poor ductility and does not adhere well to the inorganic matrix, it is thought that composite members to which alumina particles or alumina fibers are added as aggregate exhibit reduced bending stress.

[Example 2]
(Preparation of test samples)
<Example 2-1>
Using the same manufacturing method as in Examples 1-3, a test sample for this example was obtained by adding 50% by volume of aluminum fibers to an inorganic matrix made of boehmite.

<Comparative Example 2-1>
As the aluminum powder, aluminum powder manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was prepared. The aluminum powder had a particle size of approximately 53 to 150 μm and an aspect ratio of 2 or less. Then, in the same manner as in Examples 1-3, except that aluminum powder was used instead of aluminum fibers, a test sample for this example was obtained by adding 50% by volume of aluminum powder to an inorganic matrix made of boehmite.
<Comparative Example 2-2>
Using the same manufacturing method as in Comparative Example 1-1, a test sample for this example was obtained in which no aggregate was added to the inorganic matrix consisting of boehmite.

(Bending strength measurement)
The bending strength of each test sample was measured in accordance with the Japanese Industrial Standard JIS T6526:2018. The bending strength of the test samples was measured using the biaxial bending test of JIS T6526. The measurement results for each test sample are shown in Figure 7. Figure 7 is a graph showing the relationship between stroke displacement and load when the bending strength of each test sample was measured in accordance with JIS T6526.

As shown in Figure 7, the test sample of Example 2-1, which contains aluminum fibers as aggregate, shows a significant improvement in maximum fracture strength (maximum bending strength) compared to the test sample of Comparative Example 2-2, which does not contain aggregate. Furthermore, although the load (bending strength) of the test sample of Example 2-1 decreased when the stroke displacement exceeded 0.15 mm, a gradual decrease in load was observed. In other words, the test sample of Example 2-1 exhibited ductile behavior due to the aluminum fibers.

In contrast, the test sample of Comparative Example 2-2, which did not contain aggregate, showed a rapid decrease in load (bending strength) to 0 N when the stroke displacement exceeded 0.06 mm. In other words, the test sample of Comparative Example 2-2, being formed by the bonding of inorganic material particles, resulted in brittle fracture.

Figure 8(a) is a photograph showing the test sample of Example 2-1 after bending strength measurement, and (b) is a photograph showing the test sample of Comparative Example 2-2 after bending strength measurement. It can be seen that the test sample of Comparative Example 2-2 after bending strength measurement has split due to brittle fracture. In contrast, it can be seen that the test sample of Example 2-1 after bending strength measurement has cracked, but has maintained its disc shape.

Furthermore, the test sample of Comparative Example 2-1, which contained aluminum powder as aggregate, showed a slight improvement in maximum fracture strength (maximum bending strength) compared to the test sample of Comparative Example 2-2, which did not contain aggregate. In addition, the test sample of Comparative Example 2-1 also exhibited ductile behavior due to the aluminum powder. However, the test sample of Comparative Example 2-1 showed a significantly lower maximum fracture strength compared to the test sample of Example 2-1. In other words, in the test sample of Example 2-1, since aluminum fibers are dispersed inside the inorganic matrix portion 10, the inorganic material particles are connected to each other by the aluminum fibers. Furthermore, the aluminum fibers and the inorganic material particles can adhere to each other due to the malleability of the aluminum fibers. Therefore, it is considered that the maximum fracture strength was increased due to the highly ductile aluminum fibers.

In contrast, in the test sample of Comparative Example 2-1, although aluminum particles are dispersed within the inorganic matrix portion 10, it is difficult for the inorganic particles to bond together with the aluminum particles. Therefore, it is thought that the maximum fracture strength was not sufficiently improved in the test sample of Comparative Example 2-1.

[Example 3]
(Preparation of test samples)
<Reference example 3-1>
Aluminum fiber (product number: TW/Al/20) manufactured by Nikko Techno Co., Ltd. was used as the test sample for this example.

<Reference example 3-2>
The same aluminum fibers and deionized water used in Reference Example 3-1 were sealed in a pressure vessel and heated at 180°C for 6 hours. After heating, the aluminum fibers were removed from the pressure vessel. In this way, the hydrothermal treatment test sample for this example was obtained.

<Reference example 3-3>
The same aluminum fibers as in Reference Example 3-1, deionized water, and ammonia were sealed in a pressure vessel and heated at 180°C for 6 hours. After heating, the aluminum fibers were removed from the pressure vessel. In this way, the test sample of this example, which had undergone ammonia-added hydrothermal treatment, was obtained.

(Microscopic observation)
The test samples of Reference Examples 3-1 to 3-3 were observed on the surface using a scanning electron microscope (SEM). Figure 9 shows SEM images of the surfaces of the test samples of Reference Examples 3-1 to 3-3 observed at magnifications of 1000x and 3000x.

As shown in Figure 9, the aluminum fibers of Reference Example 3-2, after hydrothermal treatment, show surface irregularities and the formation of multiple granular particles compared to the aluminum fibers of Reference Example 3-1, before hydrothermal treatment. Similarly, the aluminum fibers of Reference Example 3-3, after ammonia-added hydrothermal treatment, also show surface irregularities and the formation of multiple granular particles.

Figure 10 shows the results of X-ray diffraction measurement of the surface of aluminum fibers after hydrothermal treatment according to Reference Example 3-2. From Figure 10, a boehmite peak was observed on the aluminum fibers after hydrothermal treatment, indicating that hydrothermal treatment of aluminum fibers oxidizes the surface of the aluminum fibers and generates a boehmite layer. Furthermore, as in Reference Example 3-3, the hydrothermal treatment is accelerated by adding ammonia, so it is thought that a boehmite layer is also formed on the surface of the aluminum fibers in Reference Example 3-3.

Here, as in Examples 1-1 to 1-3, when a mixture of hydraulic alumina, aluminum fibers, and deionized water is heated and pressurized under conditions of 400 MPa, 180°C, and 20 minutes, it is presumed that a reaction similar to the hydrothermal treatment described above occurs in the aluminum fibers. Therefore, it is thought that a boehmite layer is formed on the surface of the aluminum fibers. Furthermore, as will be described later, when a mixture of hydraulic alumina and deionized water is subjected to pressurized heat treatment, the composition of the hydraulic alumina changes to boehmite. Therefore, in the test samples of Examples 1-1 to 1-3, it can be inferred that the inorganic matrix portion consisting of boehmite is strongly bonded to the aluminum fibers via the formed boehmite layer.

[Example 4]
(Preparation of test samples)
<Reference example 4>
First, hydraulic alumina BK-112, manufactured by Sumitomo Chemical Co., Ltd., was prepared as the hydraulic alumina. Next, ion-exchanged water was weighed to make up 80% by mass relative to the hydraulic alumina, and then the hydraulic alumina and ion-exchanged water were mixed using an agate mortar and pestle to obtain a mixture. Next, the obtained mixture was placed inside a cylindrical molding die (Φ10) having an internal space. The mixture was then heated and pressurized under the conditions of 50 MPa, 120°C, and 20 minutes to obtain the test sample for this example.

Figure 11 shows the X-ray diffraction pattern of the hydraulic alumina powder, as well as the patterns of boehmite (AlOOH) and gibbsite (Al(OH) ₃ ) registered in ICSD. As shown in Figure 11, hydraulic alumina is a mixture of boehmite and gibbsite. Although not shown in Figure 11, hydraulic alumina also contains ρ-alumina.

(X-ray diffraction measurement)
The X-ray diffraction pattern of the test sample of Reference Example 4 was measured using an X-ray diffractometer. Figure 12 shows the X-ray diffraction pattern of the test sample of Reference Example 4, as well as the X-ray diffraction patterns of boehmite and gibbsite registered in ICSD. From Figure 12, it can be seen that the test sample of Reference Example 4 is a structure mainly composed of boehmite. Therefore, from Figures 11 and 12, it can be seen that the raw material gibbsite (aluminum hydroxide) is transformed into boehmite by the pressurized heating method.

Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment.

The entire contents of Japanese Patent Application No. 2021-205323 (Filing Date: December 17, 2021) are incorporated herein by reference.

According to this disclosure, it is possible to provide composite members with excellent mechanical strength.

10 Inorganic matrix portion 20 Metal fibers (aluminum fibers)
100 Composite Members

Claims (7)

An inorganic matrix portion composed of an inorganic substance containing metal hydroxides,
Metal fibers that are dispersed within the inorganic matrix portion, have an aspect ratio of 100 or more, and have a flattened cross-section ,
Equipped with,
A composite member having a porosity of 20% or less in the cross-section of the inorganic matrix portion. The composite member according to claim 1, wherein the metal fibers are malleable and are mainly oriented in a predetermined direction within the inorganic matrix portion. The composite member according to claim 1 or 2, wherein the aforementioned metal fibers are contained in an amount of 10% or more by volume. The composite member according to claim 1 or 2, wherein the metal hydroxide and the metal fibers contain the same metal element. The composite member according to claim 1 or 2, wherein at least one of the metal hydroxide and the metal fiber contains aluminum. The composite member according to claim 5, wherein the metal hydroxide is boehmite. The composite member according to claim 6, wherein the inorganic matrix portion and the metal fibers are formed on the surface of the metal fibers and are bonded to each other via a boehmite layer different from the inorganic matrix portion.